Wireless communications systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or other multiple access techniques. For example, such systems can conform to standards such as Third-Generation Partnership Project 2 (3gpp2, or “cdma2000”), Third-Generation Partnership (3gpp, or “W-CDMA”), or Long Term Evolution (“LTE”).
In a wireless communications system, it is generally desired to maximize the capacity, or number of users, the system can reliably support given the resources. In a CDMA system, the capacity may be limited by the available code channel dimensions, which may be determined by the number of available orthogonal channelization (e.g., Walsh) codes as scrambled using a given scrambling code, e.g., a “primary” scrambling code. When it is desired to admit more users than channelization codes available, a system may employ one or more non-orthogonal channel sets, e.g., as scrambled using one or more “secondary” scrambling codes. The use of such non-orthogonal channel sets, however, means that the channel dimensions from a single transmitter station may no longer be orthogonal to each other, potentially leading to increased intra-cell and inter-cell interference in the system.
It would be desirable to provide techniques for cancelling at a CDMA receiver the interference caused by the use of non-orthogonal channel sets at a transmitter.